Plant tissue culture is a collection of techniques used to grow plant cells, tissue, organs and their components under defined physical and chemical conditions in vitro. Plant tissue culture used to create large number of clones from a single explant and it is easy to select the desirable traits. Plant tissue culture technique is very helpful in genetically modified. In addition, we can do this technique at a very short time and small spaces. Therefore, the plant tissue culture technique has many of advantages. In addition, it increases the agriculture production. The plant tissue culture divided into the cell, tissue culture and organ culture. Root culture and shoot culture are types of organ culture. One of the most important applications for the root culture is the production of secondary metabolites. They are chemical compounds have a defense mechanism to protect the plant. However, these compounds are not important for survival of the plant. There are compounds called primary metabolites these compounds are important for survival and growth. The human uses the secondary metabolites in many of application such as agriculture applications, medicinal applications and industrial applications…etc. To increase the production of secondary metabolites the bioreactors technique has been used and instead of using the root itself, you can use the hairy roots. Because they are advantageous over fast growth, low doubling time, more genetic stability and ability to self-division on hormone free medium.
Plant culture divided into the cell, tissue culture, and organ culture. As it is known that root tip culture is a type of organ culture and it has several types of applications. The most important one is the secondary metabolites. The metabolites are the sum of all biochemical reactions.(-Galvan et al., 2016) Secondary metabolites seem to be a very important topic. Secondary metabolites are chemical compounds that produced in the plants and used in several industrial products. Certainly, as we said, secondary metabolite there is also a primary metabolite. What is the difference between them?! It is thought that secondary metabolites are derived from primary metabolites so the actual difference will be illustrated in this review .In addition, during the review, I will discuss the method of increasing these compounds which known secondary metabolites. So let us start from here.
Definition and importance:
Plants produce an enormous variety of chemical compounds, which called secondary metabolites. These compounds distinct from the products of primary metabolites secondary metabolites vary according to family and species so we can use these compounds as a taxonomic marker. Secondary metabolites are considered, as byproducts of cell metabolites are not required for normal growth and development. Many secondary metabolites found in plants have a role in defense against herbivores, pests, and pathogens. This means that it is used as a defense mechanism for the plant. Some of secondary metabolites play an important role in reproductive such as smell and color. They are produced in small quantities and it is very hard to be extracted.(BENNETT & WALLSGROVE, 1994).
Examples of secondary metabolites:
Phenolic, Steroids, essential oils, alkaloids
Definition and importance
Unlike Secondary metabolites, which are not important for growth and development the primary metabolites, considered as essential nutrient. Primary metabolites are compounds, which produced during growth phase. They are very important to perform the physiological function and support in overall development of cells. They are produced in very large quantities and they are same in every species so we cannot use them as a taxonomic marker. They are play an important role in cell growth, reproductive and development. (C, 2017)
Examples of primary metabolites:
Vitamins, Carbohydrates, Proteins and lipids are some of examples
]Secondary metabolites as industrial products
Many of medicines, which used in medicine, are derived from secondary metabolites. Secondary metabolites are used as antitumor because they have the ability to kill the cancer cell or inhibit their activity. Secondary metabolites with cancer activity include (Flavonoids, quinones, alkaloids and terpenoids)
Secondary metabolites can also function to reduce inflammatory response and have the function to inhibit pathogen progression. (lin, 2017)
Secondary metabolites are used for anti-herbivore and anti-fungal effects. They have been developed for agriculture usage as insectides. For example, neonicotinoids are a group of insecticides, which are derived from alkaloid. The nicotine is derived from Tabaco. Another example is Juglone (a phenolic lactone) which secreted from walnut plant and inhibit the growth of neighboring plant species. (lin, 2017)
Secondary metabolites are responsible for flavors of many spices. Their flavors are given through accumulation of monoterpene. So they used in cooking and food industry. (lin, 2017)
Types of culture producing secondary metabolites
- Root tip culture.
- Shoot tip culture.
Mass production of secondary metabolites is conducted using bioreactors. Bioreactors are vessels made of glass or steel. They are in vitro culture, which ensure cell survival through delivery of essential nutrients for the cell. This means that the bioreactors are devices designed to grow cells or tissue in them. (Blose et al., 2014)
The bioreactors are one of the most effective ways for increasing of secondary metabolites. It is the application for large-scale cultivation for production of secondary metabolites. The cells are suspended in liquid under unique physical and chemical conditions. However, submersion of plantlets into culture has been found, cause another problem. It is causing change in morphology and physiological abnormality. It is also causing a problem with acclimatization and survival of resulting plants. Therefore, a new type of bioreactors known as temporary immersion has been developed and adapted specially for the needs of plant. (Yancheva et al., 2019)
Hairy root culture and its steps
Hairy roots are system based on inoculation with agrobacterium rhizogenes for increasing the production of secondary metabolites from the hairy roots instead of the root itself. Hairy roots are advantageous over fast growth, low doubling time, more genetic stability and ability to self-division on hormone free medium.
During the infection, process rhizogenes transfer a part of DNA (T-DNA) which located on the RI plasmid to the plant. Hairy roots appear within one to four weeks of infection. After growing more than one cm, transfer the excised roots to solid medium with antibiotic to kill the bacteria. Then transfer the hairy roots in liquid medium into bioreactor. (Hussain et al., 2012)Figure 3 steps of hairy root culture
Hairy roots cultures in bioreactors are critical step toward commercial exploitation of this culture system. However, conventional bioreactors without any modifications are usually inefficient to hairy roots culture.so it is necessary to have bioreactors that can maintain low hydrodynamic stress and high volumetric oxygen.(Hood et al., 2007)
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